1. Field of the Invention
This invention relates generally to fluid impulse turbines, and more particularly to a hydro turbine having a runner with laterally spaced circumferentially offset blades and inlets and outlets of rectangular cross section that alter the fluid flow characteristics and increase efficiency.
2. Brief Description of the Prior Art
A number of different types of turbines have been designed to cover the broad range of hydropower site conditions found around the world. The primary types of hydroelectric turbines used for generating hydroelectric power are commonly classified as "impulse" or "reaction" types. Customarily, certain types of turbines are used for specific head pressures.
Turbines used for low to medium head pressure applications are usually of the reaction type and include Francis and fixed and variable pitch (Kaplan) propeller turbines. The runner or turbine "wheel" of a reaction turbine is completely submersed in water.
Turbines used for high head pressure applications are generally of the impulse type. Impulse turbines include the Pelton, Turgo and crossflow (Mitchell-Banki) designs. Most conventional impulse turbines are designed for a specific horsepower, RPM, and water pressure.
A conventional impulse turbine is a fixed-blade turbine having a runner with curved blades rotatably disposed in a protective casing. The runner of an impulse turbine spins in the air and is driven by high-speed jets of water. Water is metered to the turbine through "needle valves" which send jets of water into the turbine blades to turn the turbine, and the casing merely controls splashing. If water flow is decreased in a conventional impulse turbine, the turbine will loose efficiency.
The main characteristic of a "crossflow" turbine (also called a Mitchell-Banki turbine) is that it has a drum-shaped runner with a series of curved blades and the runner shaft is disposed horizontally, unlike Pelton and Turgo turbines which can have either horizontal or vertical shaft orientation. In the crossflow turbine a rectangular nozzle directs a broad rectangular water jet onto the fill length of the runner. The water jet strikes the blades once flowing from the periphery to the center imparting most of its kinetic energy, and then flows outward from the center imparting a small amount of energy before leaving the turbine.
Harloff, U.S. Pat. No. 4,279,569 discloses a cross-flow turbine machine that extracts energy from a moving fluid. The fluid comprises both liquids and gases. Fluid is guided into the rotor by inlet guide means and then flows through a first rotor, through the interior, through the second rotor, through the exit, and through the diffuser to exit the machine at ambient pressure. Torque is applied to the output shaft due to the change in angular momentum of the fluid across the turbine rotor.
Drees, U.S. Pat. No. 4,368,392 discloses a water turbine for open stream use featuring a vertical-axis cross-flow turbine in which cyclically-pitching blades are supported from one end only to permit the supporting structure and power generation gear to be supported out of the water. In preferred embodiments, there is independent pitch control of the turbine blades to make the blades responsive to the instantaneous flow in their vicinities.
Ossberger et al, U.S. Pat. No. 4,579,506 discloses a horizontal-inflow, vertical-outflow cross-flow turbine having a casing, a runner, a horizontal inlet and a vertical outlet. The inlet is divided by a pivoted guide vane to form a pair of inlet passages. A horizontally extending admission passage is connected to the casing at the inlet side thereof, and a vertically extending discharge passage is formed as a draft tube and connected to the casing at the outlet thereof. The inlet and the guide vane are arranged such that the inlet flow to the runner is directed downward at an angle of about 40.degree.0 with respect to the horizontal, and the outlet flow from the runner is directed substantially vertically. At the outlet there are a pair of side spaces on either side of the runner resulting in an increased cross section conforming to the cross section of the draft tube. Both of these side spaces are vented to the atmosphere by a single venting valve so that the suction pressure in the draft tube does not exceed a predetermined value.
Miller et al, U.S. Pat. 4,464,580 discloses a hydro-electric turbo-machine having a rotor member movable relative to a stationary housing member with a ring-shaped or annular seal between both of these members which serves to seal pressurized water from an external space or region. One of both of these members possesses a sealing surface against which there is pressed a sealing body of the seal which is inserted into the other member.
Stenild, U.S. Pat. No. 5,456,585 discloses a positive displacement fluid motor having a chamber and a rotor having stiff blades which at their outer ends are provided with wings of elastomeric material fastened to the reverse side of the blades in relation to the direction of rotation. The wings are deflected by a wall part in the chamber when passing between the outlet and inlet of the chamber.
The present invention is distinguished over the prior art in general, and these patents in particular, by a hydro turbine having a housing with a cylindrical chamber and opposed end walls with laterally spaced smaller rectangular inlets and laterally spaced larger rectangular outlets formed in upper and lower portions of the chamber side wall in horizontally opposed relation. Smaller rectangular inlet ducts adjoin the inlets, and larger rectangular outlet ducts adjoin the outlets. A cylindrical runner surrounding a power take-off shaft is rotatably enclosed in the chamber and has a central cylindrical hub divided into laterally spaced hub portions with a first and second plurality of circumferentially spaced peripheral blades extending angularly outward from each hub portion, the first plurality of blades being circumferentially offset from the second. Arcuate laterally spaced upper and lower flow passageways of rectangular cross section defined between the central hub portions and circumferential segments of the chamber side wall extend between the upper inlets and outlets and lower inlets and outlets, respectively. The runner and shaft are rotated by conducting an incompressible liquid through each or selected ones of the inlet ducts and discharging it through the respective outlet ducts. The offset blades divide the rectangular flow passageways into unequal volumes such that the volume and head pressure of the incoming liquid is alternately greater or less on one side of the runner than the other side to facilitate rotation and discharge of the liquid.